The present invention relates generally to computed tomography (CT) technology, and more particularly, to a method and apparatus for optimizing the dosage applied to a scan subject to acquire imaging data. Specifically, the present invention is directed to a cone angle dependent pre-subject filter.
Typically, in CT imaging systems, an x-ray source emits a fan-shaped beam toward a scan subject, such as a patient. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array then produces a separate electrical signal indicative of the attenuated beam received by that detector element. The electrical signals are then transmitted to a data processing unit for analysis and ultimately image reconstruction.
Generally, the x-ray source and the detector array are rotated with a gantry within an imaging plane and around the scan subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for detecting the light energy from an adjacent scintillator.
There has been a general desire toward reducing radiation exposure in such systems. Reduction of radiation dosage to scan subjects is therefore desirable on CT systems. A number of imaging techniques have been developed to reduce the radiation dose directed toward a scan subject for data acquisition. However, these imaging techniques often result in higher signal-to-noise ratios and poor image quality.
It would therefore be desirable to design an imaging system that optimizes the dose of radiation projected to the scan subject for data acquisition without jeopardizing image quality.
The present invention is directed to a CT imaging system utilizing a cone angle dependent pre-subject filter to optimize dosage applied to the scan subject for data acquisition. The cone angle dependent pre-subject filter is designed to have a variable shape. In one embodiment the shape is thicker for outer detector rows and thinner for inner detector rows. As a result, x-rays corresponding to the outer detector rows undergo greater filtering than the x-rays corresponding to the inner detector rows which also evens noise distribution. All of which overcome the aforementioned drawbacks.
Therefore, in accordance with one aspect of the present invention, a cone angle dependent pre-subject filter for use with a radiation emitting imaging device is provided. The filter includes a flat surface as well as a concave surface. A number of sidewalls connecting the flat surface and the concave surface in a single solid structure are also provided.
In accordance with another aspect of the present invention, a radiation emitting imaging device includes a rotatable gantry having an opening defined therein for receiving a subject to be scanned. The device further includes a subject positioner configured to position the subject within the opening as well as a high frequency electromagnetic energy projection source configured to project high frequency electromagnetic energy to the subject. The imaging device further includes at least one filtering device configured to filter high frequency electromagnetic energy projected to the subject. The filtering device is formed of a bulk of filtering material having a non-uniform attenuation. The imaging device also includes a detector array having a plurality of detectors to detect high frequency electromagnetic energy passing through the subject and to output a plurality of electrical signals indicative of an intensity of the high electromagnetic energy detected: A data acquisition system is provided and connected to the detector array and configured to receive a plurality of electrical signals. An image reconstructor connected to the data acquisition system is provided and configured to reconstruct an image of the subject from the plurality of signals received by the data acquisition system.
In accordance with a further aspect of the present invention, a cone angle dependent pre-subject filter includes means for receiving high frequency electromagnetic energy. The filter further includes means for increasing attenuation of high frequency electromagnetic energy flux in a first region as well as means for decreasing attenuation of high frequency electromagnetic energy flux in a second region.
In accordance with yet another aspect of the present invention, a method of manufacturing a pre-subject filter for use with a radiation emitting imaging device includes the step of defining a block of filtering material. The method further includes shaping the block to have a linear surface and fashioning the block to have a curvilinear surface.